Grover Norquist is best known as the right's most fervent enforcer of anti-tax ideology, but that's actually not quite what he is. Norquist, whose most famous quote is the one about shrinking government until it's small enough to drown in a bathtub, is actually opposed to anything that raises government revenue. That's a subtle difference but a real one, because taxes in the classic sense aren't the only way to raise revenue. You can also close tax loopholes, for example. Norquist is against that. Or you could fund Medicare using my idea of running up a bill for Medicare services while you're alive and then having the government settle accounts with your estate after you're dead. This has much to recommend it from a conservative perspective (personal responsibility, skin in the game, long-term budget balancing, etc.), and it's not a tax in the usual sense. It's a deferred charge for services rendered. But Norquist would oppose that too since it raises revenue.
None of this would matter except that Norquist exercises an almost cultish power over Republican members of Congress. And as Matt Yglesias says, this is probably the biggest impediment around to a compromise agreement that would rein in the long-term budget deficit:
Follow the logic here. According to the Norquistian theology, a good small-government conservative can’t agree to close a tax loophole that’s bad public policy in order to entice Democrats into agreeing to spending cuts. You can’t achieve efficiency enhancing reforms to the tax code by using the prospect of enhanced revenue as a sweetener, and you can’t broaden the coalition for spending cuts by using enhanced revenue as a sweetener. So the tax code stays inefficient and the spending level stays high, all so the members of the True Faith can be unsullied in the purity of their complaints about the inefficiency of the tax code and the high level of spending.
That's about it. There are compromises to be had in this arena, where liberals would agree to some spending cuts and conservatives would agree to reducing tax expenditures and tax subsidies. But there's no real compromise to be had for a deal that's pure spending cuts forever and ever, and that's the only deal Republicans will accept. So government won't shrink at all, let alone to bathtub size. And yet, Grover Norquist somehow keeps his reputation as the Beltway's greatest friend of small government. Isn't politics grand?